120k Transmission - Flush or Drain

Status
Not open for further replies.
Originally Posted by BMWTurboDzl



Heat and the fact that there still is some air in the unit. The article doesn't say that the units can run forever with out an ATF change.

The article does seem to separate water/dirt from air. Breathers allowed some air but kept water/dirt out. Engineering of the breathers to reduce the amount of air to only what's required is an advancement in itself. I any case the trick to reading Wiki is to hit the citations in order to obtain a deeper understanding.


The article makes sense to me because I remember years ago where the ATF dipstick on my late model vehicles were always just kind of loose fitting.


You have to understand that the transmission will have as much air as there is free space not occupied by other things like ATF, gears etc. and it is at equilibrium with the atmospheric pressure. Not just "some" air. Some air would be referred to when a system is filled with "some" air and then hermetically sealed. That is not the case with transmissions. The breather does not limit air movement, the air movement is dictated by the inside workings of the transmission. Spinning gears will create air drafts, expanding ATF will displace air above etc. Even the initial start up will create a big air movement as the ATF is being pumped though some of the empty passages that drained during shut off period.

The breather ensures that the air is free to move in or out without ingesting water and other contaminants. It does not limit air movement, because if it did, the air would find some other way to enter/escape, but that would not be controlled, so other contaminants would likley be carried over as well, plus depending on the location, a loss of ATF.
 
I had just went through this last fall. Had about 374,000km or so on my 1993 C1500. The fluid in the 4L60E was dark brown, almost black, smelled awful but not burnt. The transmission slipped when down shifting when trying to pass on the highway. It also shuddered bad when at low speed in lockup. Using the cooling line, I did a fluid exchange with basic Dex3 and no filter change. In a few km it was shifting great and has been for several thousand more km.

This was a heavily abused truck. I knew the previous owners and left no doubt it was run hard. But how could a fluid exchange on a high mileage transmission not end badly?
 
Thanks everyonefor the input! I feel much better knowing that the tranny should be just fine... It seems like on the flush vs drain there is alot of disagreement. Therefore, I think I'll err on the side of caution. Plan is this weekend to take the car to the shop for a D&F / replace filter (Don't have lifts). From then on, D&F method for the next two times I change the engine oil, via fluid extractor in the dipstick. I like the fact that the fluid with get close to 100% clean over the 3 drains, and the cleaning agents will gradually start working.
 
Unless the transmission has been consistently abused its whole life, you are fine. I would do a simple drain & fill, then check the condition of the fluid (blotter) after 5,000 miles -- it should look a little more red than brown compared to the previous check. Do another drain & fill at that time, then keep up with the drain & fill services every 30,000 miles going forward. Again this is just what I would do based on the information provided.

If there is an option to replace the trans filter (not a "sealed" transmission), I would do that now instead of just a drain & fill. Then keep up with the drain & fill services every 30,000 miles.
 
Status
Not open for further replies.
Back
Top